The removal of bark from logs has been termed both "log barking" and "log debarking". The present inventors prefer the term "log debarking".
Log debarking techniques have been described, in general terms, in the August 1969 issue of the Australian Timber Journal, pages 43 and 45, in the book entitled "Handbook of Pulp and Paper Technology" (second edition), edited by K.W. Britt and published by Van Nostrand Reinhold Company, at pages 103 and 122, and also in the book entitled "Forest Products, their Sources, Production and Utilization", by Panshin, Harrer, Bethel and Baker, published by McGraw-Hill Book Company (second edition, 1962), at pages 332 to 335.
As will be seen from these references, it has been common practice to use a drum debarker to remove bark from logs. With a drum debarker, logs are passed through a rotating drum which has internal vanes or ribs. As the logs are tumbled within the drum, they strike each other and the vanes or ribs within the drum, and these impacts act to tear the bark from the logs.
Such drum debarkers are generally unsuitable for debarking stringy-bark eucalypts and other rough barked species. Rotary or ring debarkers have been used for this application, but with limited success. The rotary or ring debarkers have a hollow rotor unit within which are mounted inwardly projecting cutters or barking tools. The cutters or barking tools are rotated about a log as it is moved through the rotor unit to cut and strip the bark from the logs. Examples of developments in rotary debarkers are found in the specifications of Australian patents Nos. 479,105 (to Kokum Industri Aktiebolag) and 501,776 (to V.L. Valo), and in the specifications of Australian patent applications Nos. 21267/83 (Hutson) and 66304/86 (Fuji Kogyo K K).
Other debarking techniques include hydraulic debarkers using water jets under high pressure, flails (see the specification of Australian patent No. 506,204 to L.J. Emmins), "knocking" the bark from a log (see the specification of Australian patent No. 511,333 to G.A. Williames), and, of course, manual removal of the bark with axes and the like.
All of these prior art bark removal techniques and equipment have been recognised as not being entirely satisfactory, because the technique used is too slow, or too expensive, or is not really effective at stripping the bark cleanly from the wooden body of a log.